#include "MicroHook.h"

/*returns pointer to existing function*/
BYTE *MH_VTBLHook(DWORD *pVTBL, DWORD dwIdx, BYTE *pNewFunc)
{
    BYTE *pOrigFunc;
    DWORD dwOldProt;
    VirtualProtect((void*)&pVTBL[dwIdx], 4, PAGE_EXECUTE_READWRITE, &dwOldProt);
    pOrigFunc = (BYTE*)pVTBL[dwIdx];
    pVTBL[dwIdx] = (DWORD)pNewFunc;
    VirtualProtect((void*)&pVTBL[dwIdx], 4, dwOldProt, &dwOldProt);
    return pOrigFunc;
}

/*returns pointer to trampoline function*/
BYTE *MH_TrampolineAdd(BYTE *pOrigFunc, BYTE *pNewFunc, BYTE *pTrampolineFunc, BYTE bSize)
{
    BYTE bTemp;
    DWORD dwOldProt;
    BYTE bTrampEndSize;
    VirtualProtect((void*)pTrampolineFunc, bSize+5, PAGE_EXECUTE_READWRITE, &dwOldProt);
    VirtualProtect((void*)pOrigFunc, bSize, PAGE_EXECUTE_READWRITE, &dwOldProt);
    bTemp = bSize;
    while (bTemp-- > 0) pTrampolineFunc[bTemp] = pOrigFunc[bTemp];
    pTrampolineFunc += bSize;
    pTrampolineFunc[0] = 0xE9; //JMP [rel16/32]
    *(DWORD*)(pTrampolineFunc+1) = (DWORD)((pOrigFunc+bSize - pTrampolineFunc) - 5);
    pOrigFunc[0] = 0xE9; //JMP [rel16/32]
    *(DWORD*)(pOrigFunc+1) = (DWORD)((pNewFunc - pOrigFunc) - 5);
    bTemp = 5; while (bTemp++ < bSize) pOrigFunc[bTemp] = 0x90;
    VirtualProtect((void*)pOrigFunc, bSize, dwOldProt, &dwOldProt);
    return (pTrampolineFunc - bSize);
}

/*returns pointer to trampoline function*/
BYTE *MH_TrampolineRemove(BYTE *pOrigFunc, BYTE *pTrampolineFunc, BYTE bSize)
{
    DWORD dwOldProt;
    VirtualProtect((void*)pOrigFunc, bSize, PAGE_EXECUTE_READWRITE, &dwOldProt);
    while (bSize-- > 0) pOrigFunc[bSize] = pTrampolineFunc[bSize];
    VirtualProtect((void*)pOrigFunc, bSize, dwOldProt, &dwOldProt);
    return pTrampolineFunc;
}